The present invention relates to an optical three-terminal element for controlling the intensity light by the intensity of another light.
In addition, the present invention relates to an optical gate array for controlling two-dimensional data of second light by two-dimensional data of first light using such an optical three-terminal element.
A strong demand has arisen for development of an optical gate array, using an optical three-terminal element, as a key device for performing optical data processing and optical signal processing. As an element of this type, an element called "symmetric self-electrooptic-effect device (S-SEED)" has been proposed, as described in "Applied Physics Letters" volume 52, p. 1,419. In this element, two multi quantum well (MQW) pin type optical modulators formed on the same semiconductor substrate are connected in series with each other through an external electrode, and a constant-voltage power supply is connected to both ends of the series circuit of the modulators. With this arrangement, a transmitted light component of light radiated on the second pin type optical modulator is changed by the intensity of light input to the first pin type optical modulator. This element can control a transmitted light component, of light biased with a predetermined intensity, by means of input light having the same wavelength. An arrangement and characteristics of the element will be described below with reference to FIG. 38(a) and 38(b).
FIGS. 38(a) and 38(b) respectively show the arrangement and characteristics of a conventional element (S-SEED). FIG. 38(a) is a sectional view of the element. FIG. 38(b) is a graph showing the light input/output characteristics-of the element. Referring to FIG. 38(a), reference numeral 100 denotes a pin structure; 101, a p-AlGaAs clad layer; 102, an i-AlGaAs/GaAs MQW layer; 103, an n-AlGaAs clad layer; 104, an insulating layer consisting of i-AlGaAs and p-AlGaAs; 105, a GaAs substrate; 106, an insulating layer; 107, an electrode; and 108, a constant-voltage power supply. Reference symbol P.sub.in denotes input light; P.sub.bias, bias light; and P.sub.out, output light.
In such an arrangement, the pin structure 100 consisting of the p-AlGaAs clad layer 101, the i-AlGaAs/GaAs MQW layer 102, and the n-AlGaAs clad layer 103 is stacked on the GaAs substrate 105 through the insulating layer consisting of i-AlGaAs and p-AlGaAs. A side surface of the pin structure 100 is coated with the insulating layer 106. The n-AlGaAs clad layer 103 of the first pin structure 100 and a p-AlGaAs clad layer 101 of a second pin structure 100.sub.1 are connected to each other through the electrode 107. If the input light P.sub.in and the bias light P.sub.bias are respective incident on the first and second pin structures 100 and 100.sub.1 to obtain transmitted light as the output light P.sub.out, P.sub.in -P.sub.out characteristics exhibit positive logic type bistable characteristics shown in FIG. 38(b). Light intensity modulation is performed by using a quantum confined Stark effect (QCSE), i.e., modulating the transmittance of the i-AlGaAs/GaAs MQW layer 102 at its exciton absorption wavelength by changing a reverse bias voltage applied to the pin structure 100.
The following three problems, however, are posed in the conventional optical gate array.
First, the contrast ratio of each pin structure, i.e., the intensity ratio of output light P.sub.out before and after switching, is as low as 2:1 to 3:1. For this reason, in order to arrange a plurality of such elements in series to be cascade-operated, two pin structures having the same characteristics must be arranged in parallel to be differentially switched, thus requiring a complicated arrangement.
Second, input light and bias light must be independently radiated on two adjacent pin structures from the same direction, and hence an operation of an element is very difficult. For example, when a logic operation is be performed between two two-dimensional optical patterns, images must be projected on the flat surface of the array while they are kept separated and shifted from each other by an amount corresponding to the distance between the two structures. This requires a high-precision, complicated optical system.
Third, since the photodetective pin structure and the modulating pin structure have the same structure, the light input/output characteristics are limited to positive logic gate characteristics, and only a gain of about 1 is obtained.